With her pooch in tow, the Gossip Girl star celebrates her 21st b-day on the New York City set of her show. Plus: Ashlee Simpson, Lindsay Lohan, Paris Hilton and more

HOMECOMING QUEEN

Who says you can't go home again? Shannen Doherty, who will debut her scandalous return to Beverly Hills Sept. 2, makes a stunning arrival Saturday at the L.A. premiere party for 90210 in Malibu.